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Australian Human Resources Institute Diversity Awards 2013 Finalist

Mark Phillips (Las Campanas Observatory)

"Near-Infrared and Echelle Observations of Type Ia Supernovae"

Abstract. Type Ia supernovae (SNe Ia) are one of the most effective observational tools for measuring the expansion history of the Universe. However, SNe Ia are not homogeneous in luminosity. Rather, their successful use in cosmology is due to the discovery of empirical relations that dramatically decrease the dispersion in peak luminosities at optical wavelengths. These complications can largely be avoided by working in the near-infrared (NIR), where dust extinction corrections are much smaller than in the optical, and where the luminosity-light curve shape dependence observed in the optical can also largely be ignored. The combination of optical + NIR photometry shows that SNe Ia have Rv values that span the range from ~1.5-3 that may be a function of the amount of reddening itself. The application of individual values of Rv rather than a global average leads to significant improvements in the dispersion of the Hubble diagram at optical wavelengths. Echelle observations can be used to probe the source of the dust reddening of SNe Ia. Measurements of the strength of the diffuse interstellar band at 5780 Angstroms indicate that the dust is predominantly located in the ISM of the host galaxies, and not in circumstellar material. However, ~25% of SNe Ia display anomalously-strong Na I column densities in comparison to the amount of dust extinction derived from their colors.

Held in the AAO Meeting Room (Room 7, 1st Floor, Building 2) at 11:00 AM on Tuesday, 04 June 2013